Extrudable fluorocarbon propellants

ABSTRACT

PROPELLANT COMPOSITIONS ARE PREPARED CONTAINING METALS, OXIDIZING AGENTS AND A COPOLYMER OF VINYLIDENE FLUORIDE AND PERFLUOROPROPYLENE WITH POLYTETRAFLUOROETHYLENE.

United States Patent 6 Int. Cl. C06d /06 U.S. Cl. 149-19 7 ClaimsABSTRACT OF THE DISCLOSURE Propellant compositions are preparedcontaining metals, oxidizing agents and a copolymer of vinylidenefluoride and perfiuoropropylene with polytetrafluoroethylene.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

The present invention relates to improved fluorocarbon propellantcompositions.

In the last few years considerable interest has developed in thefluorocarbon family of polymers as potential binder materials forcomposite solid propellants. Binders for composite solid propellantshave, historically, consisted of natural or synthetic plastics, resins,or elastomeric materials composed of the elements carbon, hydrogen,oxygen, and nitrogen. Because of their high density, thermal stability,water impermeability compatibility with a Wide range of propellantingredients, and high heat of reaction with metals, the fluorinatedbinders exhibit many desirable properties in the propellant field. Theycan be divided into two classes, those which are castable and thosewhich must be processed by extrusion or compression molding New highdensity solid propellants and their preparation utilizing a singlefluorocarbon as a binder are described in copending patent applicationSer. No. 99,967 filed Mar. 31, 1961. These propellants which contain ametal-hydride as the fuel and ammonium perchlorate as the oxidizer, areprocessed by isostatic pressing. The present invention is for improvedfluorocarbon composite propellants which have better chemical andphysical properties than other known solid propellants.

It is an object of the present invention to provide a solid propellantwith a high density impulse along with a relatively high specificimpulse.

Still another object is to provide a propellant with exceptionally highstructural integrity.

A further object of this invention is to provide a propellant which haslong storage life under varying temperature and humidity conditions.

Yet another object is to provide a propellant which can be produced inlarge volumes at low cost.

Another object is to provide a propellant with a wide range of burningrates and physical properties without changing over-all composition orenergy level.

Another object of this invention is to provide a propellant for use inseatejection and cockpit-capsule-ejec tion devices or other deviceshaving high inert mass to propellant volume ratio.

Other objects and many attendant advantages of this invention will bereadily appreciated as the same become better understood from thefollowing disclosure.

The present propellant composition comprises from 5 to 60 percent binderwhich is composed of polytetrafluoroethylene (hereinafter referred to byits trade name Teflon) and a copolymer of vinvlidene fluoride andperfluoropropylene (hereinafter referred to by its trade name Viton), inweight ratios of from 3:1 to 1:10; from 10 to percent by weight oxidizerselected from the group consisting of ammonium perchlorate, lithiumperchlorate, potassium perchlorate, cyclotetramethylene tetranitramine,nitronium perchlorate, hydrazine, diperchlorate, hydrazine nitroform andhydroxylamine perchlorate; from 0 to 90 percent by weight metallic fuelselected from the group consisting of aluminum, magnesium, zirconium,hafnium, tungsten, thorium, beryllium, uranium, boron, titanium,aluminum hydride, beryllium hydride, zirconium hydride alloys andmixtures thereof; from 0 to 30 percent by weight of a member selectedfrom the group consisting of triaminoguanidine, triaminoguanidine azide,double salt triaminoguanidine azide-hydrazine azide, and mixturesthereof.

In preparing these formulations the Viton is first dissolved in asolvent selected from a low-boiling ketone such as acetone andmethylethylketone or a low boiling ester such as ethyl acetate, methylacetate and butylacetate, and nitroalkanes such as nitraethane. TheTeflon and other ingredients (oxidizer, fuel, and additives) are thenthoroughly mixed into the Viton solution to form a uniform slurry. Theslurry or suspension is washed for from 5 to 10 minutes with hexane, thevolume of hexane being from one to four times the volume of slurry.After the suspension has settled the supernatant hexane is decanted orsiphoned off and the resulting residue is dried under ambient conditionsfor 8 to 24 hours. The material is now ready for extrusion in a standardpropellant extrusion press.

The slurry may be washed with normal hexane or other low boiling liquidhydrocarbon two or three times, as necessary. Other wash materialsdepending on solubility of propellant ingredients are Freons andchlorocarbons.

The following examples are given for a better understanding of thisinvention and no unnecessary limitations are to be understood therefrom.

The burning rate of the above composition at 1000 p.s.i. 70 F., was 0.35in./sec.

EXAMPLE III Ingredients: Percent by weight Teflon 10 Viton A l5 Ammoniumperchlorate 55 Aluminum powder 20 This propellant was static-fired inboth 2-inch and 5- inch diameter evaluation motors at 65, 70, and F. Thespecific impulse at 70 F. was 235 lbf.-sec./lbm., corrected to 1000/14.7. The performance of this propellant was also demonstrated in twoflight tests of 5-inch motors, at a ratio of inert mass to propellantvolume of 550 lb./cu. ft. These motors flew 10,515 and 10,575 yardsrespectively, while control rounds using a state of-the-art polyurethanepropellant flew an average of 8,350 yards.

3 EXAMPLE 1v Ingredients: Percent by weight Viton A 15 Teflon 5 Ammoniumperchlorate 65 Beryllium 15 EXAMPLE V Ingredients: Percent by weightViton A 15 Teflon 5 Ammonium perchlorate 42.4 Zirconium (22 37.6

The above propellant composition was successfully static-fired in 5-inchdiameter motors at 65, 70, and 165 F., and was evaluated in two flighttests in 5-inch hardware at a mass-to-volume ratio of 550 lb./cu. ft.These motors flew 11,350 and 11,020 yards respectively. This representsan average increase in range of 34% over that of control roundscontaining the same volume of a state of-the-art polyurethane propellantand an increase over the range attained by the higher impulsealuminum-fluorocarbon propellant described in Example III above.

This same composition using zirconium particles of 5;; increased theburning rate by a factor of 3. By varying the weight ratios of the 22and 5 particles of zirconium, a burning rate of .34 in/sec. to 1 in/sec.was achieved.

EXAMPLE VI Ingredients: Percent by weight Viton A 20 Teflon 20 Ammoniumperchlorate 30 Zirconium (22 30 The above composition has high densitywith less than solids in the exhaust products. This is an example of theuse of fluorine in the binder as an oxidizer to form gaseous metalproducts in place of liquid or solid oxides. This formulation issuitable for spin application where some solids inthe exhaust productsdeposit in the combustion chamber.

EXAMPLE VII Ingredients: Percent by weight Viton A l5 Teflon Ammoniumperchlorate 30 Zirconium (22 40 The above propellant composition isapproximately optimum (at that binder level and binder composition) onthe basis of burnt velocity at a mass-to-volume ratio of 1000.

EXAMPLE VIII Ingredients: Percent by weight Viton A 15 Teflon 10Ammonium perchlorate 44.4 Zirconium (22 30.6

This composition was successfully fired in 5" 38 RA-P projectiles(Rocket Assisted Projectile) and withstood 21,000 centrifugal Gs. It isan example of a propellant that can endure severe environmentalconditions and remain structurally intact. This has been demonstrated ingrains ranging from 1" to 3 /2" in diameter.

EXAMPLE IX Ingredients: Percent by weight Viton A 12 Teflon 8 Nitroniumperchlorate 45 Triaminoguanidine 15 Aluminum The above composition is anexample of fluorocarbon binder compatability with highly energeticpropellant ingredients.

4 EXAMPLE X Ingredients: Percent by weight Viton A 7 Teflon 4 Magnesium4 Ammonium perchlorate 10 Tungsten (6.5

The above composition was extruded into 5-inch propellant grains. It hada measured density of 5.76 g./cm. a measured specific impulse of 72lb.-sec./ lb. and a specific impulse efficiency of 69% in a 5-inch motorbecause of a large percentage of nongases in the exhaust jet. Althoughthis composition was formulated for use in Tailored Exhaust VelocityRockets (TEVR), it out-distanced stateofthe-art polyurethanepropellants.

EXAMPLE XI Ingredients: Percent by weight Viton A l2 Teflon 8 Nitrogenperchlorate 50 Aluminum 5 Aluminum hydride 25 This is a typical exampleof a high specific impulse propellant using fluorocarbon binders inaccordance with this invention.

EXAMPLE XII Ingredients: Percent by weight VitonA 15 Teflon 15 Potassiumperchlorate 50 Aluminum 19 Boron 1 This is an example of a thermallystable propellant.

EXAMPLE XIII Ingredients: Percent by weight Teflon 12.8

Viton A 19.2 Ammonium perchlorate 63.0 Aluminum 5.0

The specific impulse of the above composition at 70 F. was 230lbf.-sec./lbs., corrected to 1000/l4.7.

EXAMPLE XIV Ingredients: Percent by weight Teflon 15 Viton A 22.5Ammonium perchlorate 62.5

The specific impulse of the above composition at 70 F. was 214lbf.-sec./lbm., corrected to 1000/ 14.7.

EXAMPLE XV Ingredients: Percent by weight Teflon 5 VitonA 15 Aluminum 25Hydrazine diperchlorate 55 In carrying out the invention a preform orarticle such as a solid rod or internal star-perforated grain may beformed by pressing, by rolling, or by extrusion. The Viton- Teflonbinder markedly reduces the temperature and/or pressure necessary toprocess and extrude the propellant in a finished well consolidated form.

Both aluminum and zirconium fuels with ammonium perchlorate as oxidizerin the Teflon-Viton binder system have produced high performancepropellants. The aluminum composition yields higher specific impulsesthan those containing zirconium, but the latter have significantlygreater densities. The choice of fuel depends on the characteristics ofthe system in which the propellant is to be used. The use of smallamounts of tungsten in the formulation increases the density impulsewithout greatly sacrificing specific impulse. Incorporating beryllium inthe fluorocarbon binder yields the highest specific impulse of any ofthe metallic fuels.

Optimization of the fuel system requires consideration not only oftheoretical performance calculations by also of such practical factorsas processability, mechanical properties and efficiency of combustion.

A large number of performance calculations were made, covering not onlya wide range of fuel/oxidizer/binder ratios but also a variety of bindercompositions in terms of the ratio of Teflon to Viton. The effects ofcompositional changes on both specific impulse and burnt velocity weredetermined. Because the effects of density on performance are greatestat high mass-to-volume ratios, the value of 1000 lb./cu. ft. was chosenas being typical of the volume limited systems in which this family ofpropellants would be most useful. By varying the amount of binder(consisting of 50% Teflon and 50% Viton) it was found that the 1520%binder level is near optimum for obtaining the highest specific impulse,but that 10%; or less binder is desirable for obtaining the maximumburnt velocity. However, for a practical system, 20% binder is about theminimum amount which can be used, based on consideration ofextrudability and mechanical properties. In the zirconium system,something over 30% binder is required to achieve maximum theoreticalspecific impulse. Reduction in the average particle size of the metalfuel or oxidizer results in a significant increase in both strength andmodulus and in a slight decrease in elongation. The effects of Teflonparticle size appears to be in the opposite direction. The use of largersized Teflon increases the modulus significantly, and the strength to alesser extent, while decreasing the elongation slightly. The Teflon thusacts as a binder, as well as a filler, since it can undergo appreciableelongation.

Zirconium metal powder is known to be sensitive to static electricitybut it was found that the 22-micron powder which was generally used inthis invention could be handled safely with normal precautions. However,a finer grade (a particle size) presented a serious hazard, since itselectrostatic sensitivity was 1000 ergs or less. Use of the finer metalresults in a rapid increase in burning rate. In order to use thismaterial, it was necessary to desensitize it.

Other fluorocarbon polymers may be used as alternatives for Viton A inthe Teflon-Viton binder. A similar oopolymer selling under the tradename Fluorel (hexafluoropropylene-vinylidene fluoride) or thehomopolymer of chlorotrifluoroethylene, generally known as Kel-Felastomers, and nitrosorubber provide properties about as good as theViton. Also the copolymer of tetrafluoroethylene and hexafluoropropyleneknown to the trade as Teflon 100 was used as an alternative forpolytetrafluoroethylene (Teflon) in preparing the binder.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A propellant composition comprising the following:

Ingredients: Percent by weight Copolymer of vinylidene fluoride andperfluoropropylene 15-20 Polytetrafluoroethylene 5-20 Ammoniumperchlorate 30-45 Zirconium 30-40 Ingredients: Percent by weightCopolymer of vinylidene fluoride and pcrfluoropropylene l2Polytetrafluoroethylene 8 Nitronium perchlorate 50 Aluminum 5 Aluminumhydride 25 6. A propellant composition comprising the following:

Ingredients: Percent by weight Copolymer of vinylidene fluoride andperfluoropropylene l2 Polytetrafluoroethylene 8 Nitronium perchlorate 45Triaminoguanidine 15 Aluminum 20 7. A propellant composition comprisingthe following:

Ingredients: Percent by weight Copolymer of vinylidene fluoride andperfluoropropylene 7 Polytetrafluoroethylene 4 Magnesium 4 Ammoniumperchlorate l0 Tungsten References Cited UNITED STATES PATENTS 3,027,2833/1962 Bice 149-19 3,067,074 12/1962 Gey l49'l19 3,122,462 2/1964Kaufman 149l9 3,235,421 2/1966 Berenbaum et al. l49l9 3,257,248 6/1966Short et al l4919 3,513,043 5/1970 Burnside 14919 BENJAMIN R. PADGETT,Primary Examiner US. Cl. X.R. 149-20, 21, 36, 114

